There is an increased interest in Hypertext Transfer Protocol (HTTP) streaming techniques, in particular for distribution of video to clients via mobile networks, i.e., Radio Access Networks (RANs), allowing for bitrate adaptation and streaming of live content. This is achieved by providing media content to clients in the form of media segments, i.e., files, each media segment containing media content of certain duration, e.g., five or ten seconds.
Client devices are provided with a manifest file which lists available representations of media content and where to fetch them by means of Uniform Resource Indicators (URIs). By providing different representations of the same content, e.g., having different qualities and corresponding media bitrates, clients may dynamically adapt the bitrate by selecting an appropriate representation on a segment-by-segment basis. Typically, the manifest file is fetched at least once at the beginning of the streaming session and may be updated during an ongoing session.
The media segments are provided by a media server and continuously fetched by clients, using HTTP, where they can be merged into a continuous media stream. If the available link bitrate, i.e., the bitrate which is supported by the radio link through which the client communicates with the RAN, changes, the client may select a different representation having a lower, or larger, media bitrate. In this way, use experience may be maximized while network conditions are taken into consideration. Adaptive HTTP Streaming (AHS) techniques typically require the client to measure the available link bitrate and to select an appropriate representation from the manifest file, i.e., a representation which can be delivered safely using the available link bitrate, for download.
The 3rd Generation Partnership Project (3GPP) has standardized AHS, which has been extended by the Motion Picture Experts Group (MPEG) to Dynamic Adaptive Streaming over HTTP (DASH). DASH is also being used as basis for HTTP streaming in Release 10 of 3GPP, called 3GP/MPEG DASH. Other solutions for HTTP streaming are, e.g., HTTP Live Streaming (HLS) by Apple, Smooth Streaming (ISM) by Microsoft, and Adobe Dynamic Streaming.
Different file formats are used for the media segments, such as MPEG2-TS or ISO BMFF, e.g., MP4. Known formats for manifest files are, e.g., Media Presentation Description (MPD) for DASH, ‘m3u8’ for HLS, and ‘ismc’ for ISM.
From a network perspective, in particular RANs, it is desirable to control the bitrate of media streams so as to limit the resources which need to be allocated to streaming clients, and to use the available air interface resources more efficiently. For instance, the transmission of media segments to a client may be throttled, or shaped, by pacing the transmission, thereby forcing the client to select a lower quality representation. However, since only a limited number of discrete media quality levels are available, a media stream which is transmitted to a mobile client may not fully utilize the available link bitrate. Further, pacing the transmission prevents the RAN from allocating links which support even higher bitrates and which would use the air interface more efficiently.